The design of electrical power distribution infrastructure (“electricity grid”) has evolved over decades to ensure that the electrical power that customers receive meet certain quality standards relating to voltage, frequency, and reliability.
In recent years, an increased penetration of solar power and other intermittent power generation sources in the electricity grid are causing significant control problems. For example, connected solar capacity as low as 10% of peak capacity on a distribution feeder line may result in voltage violations that are beyond ANSI-defined limits. This intermittent generation capacity must be balanced with either load or generation adjustments elsewhere on the electricity grid in order to maintain system frequency. Often, a generation facility used for balancing is located a significant distance from a feeder line containing the intermittent generation source thus resulting in significant marginal power losses, which in some cases may exceed 30%.
Also, intermittent power generation tends to cause voltage changes that can result in poor customer power quality and excess wear on substation tap changers. These substation tap changers incur increased maintenance needs and failure rates resulting from increased use caused by the intermittency. To avoid conflict between utility voltage management systems and voltage regulation capability on solar inverters, as well as to avoid potential poor regulation caused by customer equipment, intermittent generator operators have been forbidden from regulating the system voltage (IEEE 1547 and California Rule 21). Instead, electrical utilities have been monitoring line voltages and installing some in line capability to manage voltage where needed. This approach tends to be slow in response time, and costly for the utility to implement.
Conventional electrical distribution systems are not designed to accommodate the increasing amount of intermittent generation, and new solutions are sought to address these challenges.